To redeem your EaseUS Partition Master Professional key please first download and install the trial version of Partition Master Professional via the link here
After installing the trial software for Partition Master Pro, launch the program and click on the Activate button in the top right hand corner of the menu.
You should see an Activation succeeded message once you enter the key. Your activation key will grant a single license for one device for use with the software. If you run into any trouble, please refer to EaseUS Support here.